Development of a cavity-enhanced absorption spectroscopy based heavy water leak monitor for nuclear reactors

The development of a compact, low-cost instrument for reliable, continuous detection of leaks of heavy water in pressurized heavy water reactors (PHWRs) by selectively detecting semi-heavy water (HDO) in air is presented. The device employs cavity-enhanced absorption spectroscopy by targeting a specific rovibrational transition of HDO to achieve high sensitivity and selectivity. The complete development of the cavity-enhanced absorption spectroscopy based HDO in air monitor (CHArM), from laboratory feasibility studies to a field-deployable prototype, is described. This includes the optical design, instrument configuration, calibration methodology, and performance evaluation. Major technical challenges faced during development and the solutions implemented for stable, long-term operation are discussed. The CHArM instrument has achieved a measurement precision of ±10.6 ppbv for HDO in air, which is a considerable improvement over the best sensitivities reported for HDO detection instruments used in PHWRs. It offers a simpler, cost-effective, and easily deployable solution for continuous heavy water leak monitoring in PHWR settings.